Antarctic Mosses

Antarctic Mosses

Literature Review for Graduate Certificate on Antarctic Studies 2001-02

Gateway Antarctica, University of Canterbury

Dr. Lars Brabyn

Department of Geography

University of Waikato.

Abstract:

A literature review on Antarctic mosses was undertaken to identify the types of

mosses found in Antarctica and the main environmental determinants of their

habitats. This information was then discussed in relation to constructing a

Geographical Information System habitat model. Mosses reproduce asexually in

Antarctica because of the harsh conditions therefore endemism is unlikely. The

main limiting determinants of habitat are factors such as temperature, available

moisture, exposure to solar radiation and wind, and soil type. The main habitats

are in Antarctic Peninsula, Ross Island, and coastal seasonally ice free areas.

Mosses are more sensitive than lichens and cyanobacteria to climate change and

therefore are a good indicator of global climatic change. Many of the determinants

The Antarctic Environment

Antarctica has an extremely cold, dry and inhospitable climate, but nevertheless,

some plants do manage to survive in isolated areas in the dry valleys, the Antarctic

peninsula, the offshore islands and along parts of the coastline. The amount and

variety of vegetation in Antarctica is limited by several factors, namely,

temperature, available light, nutrients, and available water. As the Antarctic climate

is so extreme, all plant species are frost tolerant, with some being able to photo-

synthesise at temperatures below freezing. Access to nutrients for terrestrial plants

is problematic, because in those areas where the soil is permanently, or seasonally

exposed, the available water is very limited in such an arid climate. Sufficient

available light for photo-synthesis is limited to the Summer months, and for most

species, growth within this brief period is further constrained by snow cover, which

may not melt until mid-Summer.

Mosses

This literature review focuses on mosses as a possible tool in detecting both past

and future climate change. Although not as widespread as algae or even lichens,

mosses are represented in Antarctica by several species; Bryum a/gens,

antarcticum, argentium, Sarconeurum glaciale. In contrast to algae, lichens, and

cyanobacteria, mosses are perhaps more sensitive to climatic variation, particularly

changes in temperature and precipitation.

The isolation of colonies of Antarctic mosses to separate ice-free areas has not

This is because the harsh Antarctica climate pre-disposes most flora toward

asexual reproduction, which limits genetic variation within the species. Thus, the

recognition of endemic taxa in Antarctica is contentious. Longton (1988, 30) is

sceptical that there is any endemism: ''Of the species apparently confined to these

areas, the majority are doubtfully distinct members of different genera such as

Bryum and Ceratodon" .

Literature Review Related to Antarctic Mosses

There has been few publications specifically devoted to mosses on the Antarctic

continent. Nevertheless, some of the more general research provides useful

information on the distribution and environmental constraints on polar bryophites.

Longton (1988) focuses on not only both mosses and lichens, but the geographic

extent of the study includes both Arctic and Antarctic environments. In the Antarctic

region, the study extends to the offshore islands and out to, and beyond the

Antarctic Convergence to encompass the Macquarie, Crozet, Falkland and

Fuegian Islands. The author divides polar environments into four categories (mild,

cool, cold, frigid) in order to compare the two polar temperature regimes, but only

the' 'frigid" regime applies to continental Antarctica. Longton discusses the various

constraints to the growth of Antarctic mosses, including temperature, moisture,

solar radiation, nutrients, competition and mechanical damage from wind and

grazing. A further limiting factor, which applies much more to Antarctic, rather than

Arctic environments, is the paucity of routes of colonisation or re-colonisation of

Smith (1994) studied vascular plants (rather than mosses) on the Argentine Islands

as bioindicators of possible warming in the Antarctic region. There are only two

native vascular plants on the continent (Co/obanthus quitensis and Deschampsia

antarctica) and these may be a more sensitive indicator of change than non-

vascular species, such as mosses. The study, conducted between 1964 and 1990,

concluded that the peripheral Antarctic environment seems to be warming (Smith,

1994, 326-327). While increasing temperatures would also be conducive to the

growth of mosses, it is not clear what other factors associated with climate change,

such as available moisture and plant competition would have on the distribution of

mosses in this environment.

The study by Moorhead and Priscu (1998) centres on the environment of the

McMurdo dry valleys. The vegetation examined seems to be confined to mats of

cyanobacteria in some of the streams of glacial melt-water which flow into the

valleys. No mention is made of mosses, and it seems unlikely that this environment

would be suitable for the growth of bryophites: Although the ground would be

largely ice-free, the mosses are sensitive to drying out and there would be little

available water for terrestrial plants during the short growing season (the annual

precipitation is under 1Ocm, falling as snow in winter (Moorhead and Priscu, 1998,

352)).

Kappen (2000) focuses on the apparent competitive advantage that Lichens have

in certain parts of Antarctica. Unlike the mosses, lichens are capable of a feeble

photo-synthesis at sub-zero temperatures, such as while under a light covering of

snow (Kappen, 2000, 316-319). Furthermore, the lichens are also more capable of

2000, 321). In the arid environment of Antarctica, this relative advantage is

reflected in the number of endemic species of lichen (estimated at between 30-

80%, Kappen, 2000, 321) compared to that of mosses (estimated at 7%, Kappen,

2000, 321).

The study by Howard-Williams, Pridmore, Broady, & Vincent (1990) concerns

cyanobacteria in ponds formed on the McMurdo ice shelf and represents an

environment which is most unlikely to support the growth of mosses.

Broady (1989) studied three seasonally ice-free environments adjacent to the

Antarctic continent (Capes Bird, Royds and Crozier on Ross Island). When the

sea-ice breaks up, the catabatic winds drive a considerable amount of seas-spray

on to the adjacent land, and the amount of saline aerosols in this region affected

the growth of all flora. Mosses were found in scattered patches at all three sites,

and the limiting factors seemed to be moisture (mosses were not present above a

free-draining sub-stratum), wind (most clumps were found on slopes with a north-

easterly aspect, away from the prevailing south-easterly winds), and salinity (moss

clumps were not found in areas with high salinity caused by sea-spray, or

concentrations of penguin droppings). Despite the mosses' intolerance of high

salinity, they are relatively tolerant of moderate levels, compared to that of lichens,

and thus have a competitive advantage in areas with sufficient moisture. Isolated

cushions of mosses were found up to 900m, but most were confined to elevations

of less than 300m (Broady, 1989, 93): The constraint of elevation would represent

lower temperature, less available moisture, and greater wind exposure with

Vestal (1993) describes the difficulties of any colonising flora in establishing in

Antarctica, including the extremely short metabolically active periods each year.

Any study of plant succession would therefore have to operate on a much longer

time-scale to that of more temperate climates.

Walton (1993) mentions the part played by mosses in trapping mineral particles

washed down by Antarctic snow-melt. As well as providing a source of nutrients,

the entrapped fine particles help to provide a stable and weighty base to resist the

clump being swept away by wind or water.

Constructing a GIS model for Antarctic mosses

Several factors determine the location and abundance of Antarctic mosses, and at

least some of them may be determined indirectly using existing remote sensing

and cartographic data.

Latitude

Mosses are at the limit of their environmental range in Antarctica, and their

prevalence, and diversity decreases with increasing latitude.

Ice/Snow Cover

All areas with permanent ice cover can be eliminated as potential locations for

mosses. Unlike the Algae or Lichens, Mosses do not photo-synthesise at sub-zero

above-zero temperatures, and which do not have a similar period of no ice/snow

cover can be eliminated as possible habitats.

Soil/Rock Colour

Periodically ice-free areas with a dark soil colour will retain more solar heat during

summer and would be more likely to provide a suitable environment. Areas with

high albedo can therefore be eliminated as potential locations.

Soil/Rock Structure

Mosses have a rudimentary root system, which limits their access to nutrients and

their ability to anchor themselves to the substrate. While the immediate access to

nutrients can be a factor during initial colonisation, the clump-like structure of

established mosses usually allows the accumulation of small particles around the

base of the colony, which helps to stabilise the clump by weight, rather than by

anchoring with a deep root structure. These limitations in this taxa's ability to

anchor the clumps leaves them vulnerable to uprooting by the strong catabatic

winds. Unlike the lichens, mosses do not appear to cause a significant amount of

mechanical and chemical breakdown of their mineral substrate (Walton, 1993, 40-

46). This factor would appear to predispose the mosses to either a soil/rock

structure with pre-existing cracks in which to anchor, and/or to a location which

was protected from winds. However, many sheltered locations would also receive

less solar energy because of shading, and would therefore not provide suitable

moderate North-facing slope without other adjacent land masses to obscure the

summer sunlight.

Moisture

Unlike Lichens, Mosses cannot survive drying out, so areas which experience arid

conditions during the summer months, such as the dry valleys, can also be largely

eliminated. In this environment, local colonies of mosses may exist where streams

of melt-water provide a sufficiently stable source of moisture.

Salinity

The growth of Mosses is inhibited by high salt levels, and the study by Broady

(1989, 79-80

&

of seasonally open sea will receive a significant amount of wind-borne salt spray

generated by the catabatic winds, these areas can also be ruled out as possible

habitats for mosses. Broady's study also shows that high levels of salinity are

generated by penguin rookeries (1989, 80). Nevertheless, mosses are more

tolerant of moderate levels of salinity than lichens.

Other Factors

Other factors which may determine the distribution of mosses may be more difficult

to deduce from remotely-sensed data. Competition from other flora, such as the

Bryophitic lichens, may represent either an overall competitive advantage, or the

have an advantage over mosses in colder and drier conditions, and as Antarctic

mosses tend to replicate asexually, they would not have a local bank of reserve

spores with which tore-colonise areas after adverse short-term fluctuations in

temperature and moisture levels. Furthermore the paucity (or absence) of endemic

species could mean that any adaptation to local environmental conditions by

mosses is either impossible, or at least, unproductive (i.e., mosses may be simply

incapable of any modification which would improve their survival in this harsh

environment). The present distribution of mosses may reflect, to some extent, the

distance from reserve sources of potential vegetative colonists, i.e., distance from

nunataks, and the milder environments of the off-shore islands and the Antarctic

peninsula.

Mosses as Climatic Artefacts

A model constructed on present-day environmental variables may predict with

some degree of certainty where mosses are likely to be found in Antarctica. No

doubt, there would be exceptions, because of factors which are difficult to model,

but in such an extreme environment, even a single contra-indicating factor would

probably be enough to prevent the local establishment of mosses. Conversely, the

actual location of mosses (and other flora) on the Antarctic mainland could be used

to extrapolate past climatic history. Given the marginal growing conditions for most

flora; the constraints on seed and spore production and dispersal; the limited

animal grazing and disturbance; and the rate of vegetative growth during the short

growing season, useful speculations could be made about relatively recent and

much slower than in more benign climates and the sources of re-colonisation are

very limited, so historic modelling would seem more feasible.

Bibliography

Broady, P.A, 1989, Broadscale Patterns in the Distribution of Aquatic and Terrestrial Vegetation at Three Ice-Free Regions on Ross Island, Antarctica, Hydrobiologica 172: 77-95

Howard-Williams, C., Pridmore, R.D., Broady, P.A. & Vincent, W.F., 1990, Environmental and Biological Variability in the McMurdo Ice Shelf System, in Kerry, K.R. & Hempel, G. (eds.), Antarctic Ecosystems: Ecological Change and Conservation, Springer-Verlag, Berlin

Kappen, L., 2000, Some Aspects of the Great Success of Lichens in Antarctica, Antarctic Science 12 (3) 314-324

Longton, R.E., 1988, Biology of Polar Bryophytes and Lichens, Cambridge UP, Cambridge

Miles, J. & Walton, D.W, (eds.) 1993, Primary Succession on Land, Blackwell, Oxford

Moorhead, D.L., & Priscu, J.C., 1998, The McMurdo Dry Valley Ecosystem: Organisation, Controls, and Linkages, in Priscu, J.C. (ed) Ecosystem

Processes in a Polar Desert: The McMurdo Dry Valleys, Antarctica, Antarctic Research Series 72: 351-363.

Richardson, D.H., 1981, The Biology of Mosses, Blackwell, Oxford

Smith, R.I.L., 1994, Vascular Plants as Bioindicators of Regional Warming in Antarctica, Biologica, 99: 322-328

D.W, (eds.) Primary Succession on Land, Blackwell, Oxford

Vincent, W.F. & Ellis-Evans, J.C. 1989, High Latitude Limnology, Kluwer, Dordrecht